1Field of the Invention
The present invention relates generally to a data processor operating with a program and more particularly to a data processor having a great number of registers incorporated therein.
2. Description of the Prior Art
As a first technique known heretofore which is relevant to the present invention, there can be mentioned a system disclosed in "Motorola MC68020 User's Manual", Prentice-Hall Inc., 1984 APPENDIX B, pp. 110-112.
In the hitherto known microprogram type data processor (or microcomputer) such as exemplified by the above-mentioned system, there are employed an instruction for saving all the contents of a plurality of registers provided internally of the data processor to an external memory device on one hand, and an instruction for restoring the contents of the external memory device to the plural registers incorporated in the data processor on the other hand.
When the instructions mentioned above are used, a program being executed has to be once interrupted temporarily for saving the contents of all the registers to the external memory device in order to execute another subroutine program. Thereafter, the contents of all the registers are restored from the external memory device, whereupon execution of the program being interrupted can be resumed.
As a second hitherto known technique relevant to the invention, there may be mentioned a buffer memory control system disclosed in JP-A-56-143583.
In the case of the buffer memory control system described in this publication, it is proposed to store stack information into a high-speed buffer memory provided internally of an arithmetic controller connected to a main memory device. More specifically, stack data are stored in the high-speed buffer memory in response to an instruction "CALL" which is executed upon transition from a main program to a subprogram, while the stack data are read out from the high-speed buffer memory in response to an instruction "RETURN" which is executed upon resuming the main program from the subprogram.